The problem addressed by my invention arises especially with persons who have had operations. The extended time in which such a person must lie supine in bed not infrequently leads to the development of blood clots which are carried by the veins to the heart, and by reason of the structure of the human body through the inferior vena cava. As these clots enter the heart at least some are pumped outwardly through the artery which leads to the lungs. It is here that by reason of the numerous small passageways which characterize the lungs that the clots block certain of the blood passageways. This may lead to sudden death because here the clots act so that the blood flow to the lungs is interrupted or obstructed and the rejuvenation required by the oxygenation process cannot take place.
In the past, this problem has been met by a major surgical operation which requires a tying of the inferior vena cava and the collateral circulation which results is relied upon to provide passageways for the transmittal of satisfactory blood flow to the heart. Because this surgical operation of tying the vena cava is usually performed on a person who has already been weakened by other surgery, and by reason of the fact that it requires a rather extensive incision through the trunk area to reach the vena cava to tie it, it is considered a major and generally dangerous operation.
Anticoagulation agents are effective in many cases; nevertheless formation of blood clots in the veins of the lower extremities and migration thereof to lungs continues to be a major health hazard, especially in hospitalization, resulting in morbidity and mortality.
Mechanical devices have been developed for insertion into the vena cava by a simple catheter technique under local anesthetic, thus avoiding a major operation under general anesthesia. One such device is disclosed in Mobin-Uddin U.S. Pat. No. 3,540,431 of Nov. 17, 1970. This device is of umbrella-type configuration including skeletal framework and a hood of filtering media for lodgement in spanning relation of a vein or passageway of the human body to filter fluid flowing in a closed passageway. The undesirable features of this device are: (1) dislodgement and migration in a small percentage of patients; and (2) tendency to clogging up resulting in the development of collateral circulation. Another such device is disclosed in Kimmell U.S. Pat. No. 3,952,747 of Apr. 27, 1976. It comprises a plurality of convergent legs in generally conical array and joined at their convergent ends to an apical hub, each leg having a reversely bent hook at its end which is distal with respect to the hub. Each leg also includes a plurality of bends intermediate its length, which bends decrease the solids by-pass capability of the filter without concurrent fluid occlusion.
It has been found that such devices migrate through the blood vessel or passageway resulting in a potentially dangerous complication of internal bleeding and perforation of adjacent important organs. Also this device at times when ejected from the catheter into the vein positions itself sideways or tilted inside the passageway, with resulting increased tendency to an undesirable penetration through the vein wall.